The present invention relates to a leveler for the flattening and stress reduction of a metal strip. More specifically, the present invention is a multi-roll leveler with built-in shape control. The leveler is particularly useful, for example, in conjunction with the rolling process often utilized in the manufacturing of metal strip products.
During the manufacturing of metal sheet or strip products, various materials are combined, heated, and transformed into a molten metal compound. The molten metal is then generally molded into specific shapes, such as slabs or billets. The molded shapes may then be transported to a hot rolling mill where they can be rolled into thinner products. The molded shape may be reheated in a furnace prior to the rolling process. A molded shapes may be passed through the rolling mill multiple times. The rolling mill may convert the molded shape, typically a slab, into a thin sheet, which may then be rolled into a coil for easier handling and transport.
The hot rolling mill is useful for reducing the thickness of the molded metal slabs, and thereby producing metal strip. However, the hot rolling process may also impart undesirable shape defects to the resulting metal strip. Hot rolling mills typically flatten and thin the strip by passing it under a series of rolls. The rolls are caused to exert a force on the strip as it passes therebeneath. However, it is difficult to exert a uniform force across the width of the strip during the hot rolling process. Consequently, the finished strip may possess undesirable shape defects. These shape defects are commonly the result of stresses developed within the strip as it passes through a rolling mill and is subjected to the non-uniform application of force across its width, thereby leading to a non-uniform stretching of the length of the strip.
In light of the deficiencies of known hot rolling mills, precision levelers have been developed to equalize the length and relieve internal stresses present in the strip, thereby producing a flatter and more desirable product. These levelers are typically of two varieties: multi-roll levelers and tension levelers. Multi-roll levelers generally use opposing, substantially parallel sets of work rolls that often are supported by back-up rolls. During operation, the metal strip material is caused to pass between the opposing sets of work rolls. Each set of work rolls is placed into contact with the metal strip, such as by driving one set of work rolls toward the other, so that a leveling (flattening) force is impressed upon the metal strip as it passes therebetween. The metal strip material, which is commonly supplied in coil form, is uncoiled and fed into the entrance of the leveler. The work rolls operate to relieve any stresses induced by the hot rolling process, and to thereby impart flatness across the entire width of the strip. In contrast, tension leveling works by stretching the strip between two sets of rolls. Each set of rolls is able to grip the strip, and as the rolls rotate, tension is created in the strip. As the strip is stretched, shorter areas of the strip will become longer, and eventually uniform length and substantial flatness will be achieved across the width of the strip. As the present invention relates to a multi-roll leveler, tension leveling need not be discussed in further detail herein.
The work rolls of a multi roller leveler are typically designed to allow for bending during operation of the leveler in order to compensate for fluctuations in the profile of the metal strip. Bending is typically accomplished by using a plurality of adjusting means, such as wedges or other force exerting devices, to act on the backup rolls and, thereby, the work rolls. The adjusting means may be positioned by motor-driven jack assemblies, or other types of actuators. Because the adjusting means are generally distributed substantially across the width of the leveler, they can be used to impart a localized, non-uniform bending force on the work rolls. As such, the work rolls can be made to contact only the necessary portions of the metal strip or, to exert more or less force on particular areas of the strip.
When using a multi-roller leveler, it is necessary to determine the cross-sectional shape and, thus, the stress distribution of the strip. In known levelers, this is accomplished by manually sampling the strip and then manually setting the work rolls of the leveler accordingly. The leveler then operates on the entire strip according to the profile derived from the head or tail of the strip. This is problematic because such a manual sampling may not be truly indicative of the shape and stresses that exist along the entire length of the strip. For example, the shape defects that occur at the head or tail of the coil may not remain constant over the length of the strip. Consequently, while a portion of the strip may be properly leveled using the initial leveler settings, defects in other portions may remain. Therefore, it is desirable to be able to continuously sample the strip and adjust the leveler accordingly, so that variations in shape and stress encountered along the length of the strip are properly treated.
The present invention provides this ability. The present invention consists of a multi-roll leveler having a closed-loop control system. The leveler of the present invention utilizes a shape sensor located at the exit thereof. The shape sensor measures the stresses present in and, thus, the flatness across the width of the strip. Shape sensor readings are fed back to a microprocessor-based controller that uses the readings to ascertain and initiate necessary changes to one or more of various leveler settings. The shape sensor is preferably disposed substantially across the width of the leveler, and may be divided along its length into a number of individual measurement segments. In one particular embodiment of the precision leveler of the present invention, there are also preferably a number of work roll adjusting means disposed along the width of the leveler, such as, for example, the motor-driven jack assemblies and adjusting wedge pairs discussed above. One or more of the shape sensor measurement segments forms a measurement zone along a portion of the width of the metal strip. At least one measurement zone is preferably associated with each of the plurality of work roll adjusting means. A stress (flatness) measurement is taken by each segment of the measurement zone. The individual measurements may be averaged together or otherwise analyzed to determine the corresponding stress existing in the zone. The stress present within the particular measurement zone of the metal strip is then used by the levelers control system to calculate the amount of penetration of the work rolls necessary to flatten the metal strip in the measurement zone. The associated work roll adjusting means is then actuated to position the work rolls accordingly. This procedure is followed for each measurement zone across the length of the shape meter and the width of the metal strip. The leveler's control system may also adjust the entry and exit gaps of the leveler in response to measurement zone readings from the shape sensor. For example, the control system may signal entry and/or exit jack screws or similar devices located on the leveler, to increase or decrease the entry or exit gap between the sets of work rolls. Entry and exit gap adjustment can be used to further assist in flattening the metal strip. The shape sensor continuously monitors the treated metal strip and sends the measurement information to the leveler's control system. The closed-loop control system then adjusts the work rolls and/or entry and/or exit gaps as needed to compensate for changes in the profile of the strip. In this manner, coil-to-coil variance is improved, head scrap is reduced, and the material yield required to produce a flat strip is minimized.